A liquid processing apparatus includes a processing tank, a first electrode, an insulator, a liquid introduction port, a discharge portion, a second electrode, an opening portion, and a power supply. The first electrode is disposed at the first end of the processing tank. The insulator covers at least a part of a side surface of the first electrode disposed to protrude from an inner wall of the first end of the processing tank into the processing tank. The liquid introduction port causes a liquid to swirl by introducing the liquid in a tangential direction of the processing tank and generates a gas phase in a swirling flow of the liquid. An outer diameter of the insulator is smaller than an outer diameter of a gas-phase generating space where the gas phase is generated in the processing tank.